The invention relates to a mechanism for registering sheets of different sizes relative to a station.
Sheet registration mechanisms of various kinds are known in the art. For example, U.S. Pat. No. 4,660.819, which issued on Apr. 28, 1987, discloses a sheet registration device in a document handler of the kind used with electrographic copying apparatus wherein a set of document sheets are recirculated one or more times from the tray to a copying position and then returned to the tray. The handler of the patent has a tray surface on which sheets rest, and a sidewall or guide along one side edge of the tray surface which terminates in an inclined ramp at the surface. A similar inclined ramp is provided on the other side of the tray. The two ramps are generally parallel to each other along opposite side edges of the tray. These ramps assist in registration of the document sheets in a corner of the tray prior to feeding of the sheets to the copying position.
Known sheet registration mechanisms may require a force other than gravity to be used for proper positioning of the sheet in the registration mechanism. In the above-mentioned patent, for example, an air knife provides a jet of air which assists in locating the sheet on the tray surface. Also known, registration mechanisms require delivery of sheets to the mechanism from only one side, and such can limit the use of the mechanisms to specific kinds of apparatus.
U.S. Pat. No. 5,031,894 and U.S. Pat. No. 5,080,345, which have been assigned to the assignee of the present application, disclose a mechanism which registers a sheet of film and advances it toward an imaging station. A registration member is located along a surface that receives the sheet, and the member is engageable by an edge of the sheet for registering and guiding the sheet toward the station. An urging guide located along another portion of the surface is skewed relative to the registration member and spaced from it so that the end portions of the guide and registration member nearest the station are spaced apart sufficiently to enable the sheet to lie flat on the surface while other portions thereof are sufficiently close together to prevent the sheet from lying flat on the surface. The guide projects above the surface and is tilted away from the registration member so that the guide imparts a component of force onto a sheet resting thereon which urges the sheet toward the registration member. Both of these references discloses means for accommodating sheets of various sizes. In U.S. Pat. No. 5,031,894, movable guides pivot between a lowered position wherein they are recessed in the surface of the platen, and a raised position above the surface. When in the raised position, the movable guides are parallel to the urging guide and enable smaller sheets to be urged toward the registration member, and when in the lowered position they are substantially in the plane of the platen. This reference suggests the use of solenoids in order to raise or lower the guides. Solenoids have limited force and stroke capabilities which require the mechanism to be designed with balancing springs. Additionally, such systems are subject to frictional variations from machine to machine and, with time, such variations can cause a delicately balanced system to not operate. U.S. Pat. No. 5,080,345 pivots each guide about an axis below the platen which is perpendicular to the guides length. This results in the rear portion of the blade being raised while the front portion remains below the top surface of the platen. Due to this receding height, film sheets that are side loaded tend to have their far edge lay on top of the urging guide and not properly registered.
It is an object of the invention to provide a sheet registration mechanism which utilizes the force of gravity for locating a side edge of sheets of various sizes in the registration mechanism wherein movable guides are reliably moved between raised and lowered positions.